11000-11 in base 2

The binary number is $1100011_2$.
To convert to base 10, multiply each digit by the corresponding power of 2 and sum the results.
$1 \times 2^6 + 1 \times 2^5 + 0 \times 2^4 + 0 \times 2^3 + 0 \times 2^2 + 1 \times 2^1 + 1 \times 2^0$
$= 1 \times 64 + 1 \times 32 + 0 \times 16 + 0 \times 8 + 0 \times 4 + 1 \times 2 + 1 \times 1$
$= 64 + 32 + 0 + 0 + 0 + 2 + 1$
$= 99_{10}$

$99 - 11 = 88_{10}$

Divide 88 by successive powers of 2:
$88 \div 64 = 1$ remainder 24
$24 \div 32 = 0$ remainder 24
$24 \div 16 = 1$ remainder 8
$8 \div 8 = 1$ remainder 0
$0 \div 4 = 0$ remainder 0
$0 \div 2 = 0$ remainder 0
$0 \div 1 = 0$ remainder 0

Reading the remainders from top to bottom, we get $1011000_2$.

Alternatively, using division:
$88 \div 2 = 44$ remainder 0
$44 \div 2 = 22$ remainder 0
$22 \div 2 = 11$ remainder 0
$11 \div 2 = 5$ remainder 1
$5 \div 2 = 2$ remainder 1
$2 \div 2 = 1$ remainder 0
$1 \div 2 = 0$ remainder 1

Reading the remainders from bottom to top: $1011000_2$.